Microbes as Biofertilizers

Biofertilisers are living microorganisms that improve soil fertility by increasing the availability of nutrients to plants. They are eco-friendly alternatives to chemical fertilisers. Chemical fertilisers, by contrast, degrade soil quality and reduce microbial life in the soil.

Nitrogen-fixing microbes convert atmospheric nitrogen into usable forms, enriching the soil with available nitrogen for plant uptake.

Key Organisms:

• Rhizobium
• Azotobacter
• Azospirillum
• Frankia

Legume–Rhizobium Symbiosis:

• Rhizobium forms a symbiotic association with leguminous plants.
• This association leads to the formation of root nodules.
• Root nodules fix large amounts of nitrogen.
• The fixed nitrogen enriches the soil and benefits subsequent crops grown in the same field.

Root system of a leguminous plant

Note: The Legume–Rhizobium symbiosis is one of the most significant biological nitrogen fixation systems. Know: organism → leguminous host → site (root nodules) → outcome (nitrogen enrichment for next crop).

• Azolla–Anabaena symbiosis and cyanobacteria are widely used in paddy fields.
• They significantly increase rice yield.
• Anabaena is a nitrogen-fixing cyanobacterium that lives in association with the water fern Azolla.
• This association enriches the paddy field soil with biologically fixed nitrogen.

Azolla

L. S. of Azolla leaf showing filamentous Anabaena

• Mycorrhiza is a symbiotic association between fungi and plant roots.
• It enhances the absorption of phosphorus and other minerals from the soil.
• It also helps protect plants from pathogens.

Note: Mycorrhiza is from the Greek words for 'fungus' (mykes) and 'root' (rhiza). The fungal partner significantly extends the absorptive surface of the root system.

• Certain bacteria and fungi in the soil can convert insoluble phosphates into soluble, plant-available forms.
• This is important because phosphorus in soil is often present in insoluble forms that plants cannot directly absorb.
• These microbes release the phosphorus without any additional chemical input.

Biofertilisers:

• Improve crop yield.
• Reduce fertiliser requirement (less dependence on chemical fertilisers).
• Support sustainable agriculture.
• Aid in soil conservation.
• Are eco-friendly – they do not degrade soil quality or reduce microbial life.

• Biofertilizers are living micro-organisms that improve soil fertility by increasing the availability of nutrients to plants.
• They are eco-friendly alternatives to chemical fertilisers, which degrade soil quality and reduce microbial life.
• Nitrogen-fixing microbes such as Rhizobium, Azotobacter, Azospirillum, and Frankia convert atmospheric nitrogen into usable forms.
• Legume–Rhizobium symbiosis forms root nodules that fix large amounts of nitrogen and enrich the soil for subsequent crops.
• Azolla–Anabaena symbiosis and cyanobacteria are widely used in paddy fields and significantly increase rice yield.
• Mycorrhiza (fungus–root association) enhances absorption of phosphorus and other minerals and protects plants from pathogens.
• Phosphate-solubilising bacteria and fungi convert insoluble phosphates into forms available to plants.
• Biofertilisers improve crop yield, reduce fertiliser requirements, and help in sustainable agriculture and soil conservation.